In a typical surface-mined oil sand processing operation to produce bitumen, the oil sand is usually crushed to reduce the size of oil sand lumps. The crushed oil sand is mixed with water (e.g. in a rotary breaker) to form a slurry of bitumen, mineral solids and water, as well as to remove lumps of clay, rocks and unablated oil sand over a specified size (e.g. 2″ diameter). Then the ore/slurry is conditioned, for example, in a hydro-transportation pipeline or other conditioning means. The conditioned slurry is introduced into a primary separation vessel in which aerated bitumen droplets are separated from a bottom stream consisting primarily of water and solids. The aerated bitumen droplets are recovered as bitumen froth. The bottom stream is treated to recover as much water as possible from the final process outlet stream that is generally referred to as tailings.
The bitumen froth typically contains about 60% by weight bitumen. The remainder is mainly made up of water and solids. The froth is typically treated by adding a solvent and/or other agents, which promotes the separation of bitumen from the other components of the froth. For example, in paraffinic froth treatment processes, the bitumen froth may be mixed with a paraffinic solvent (e.g., pentane or hexane or a mixture of both) in a multi-stage counter-current decantation (CCD) process circuit (see, for example, Canadian Patent Application Nos. 2,350,907 and 2,521,248, the disclosures of which are incorporated herein by reference, which describe paraffinic froth treatment processes including CCD). In a CCD process, the bitumen froth is typically separated into:    1) a dilute bitumen phase (dilbit), mainly comprising solvent and high value components of the bitumen, known as maltenes, and dissolved asphaltenes;    2) an aqueous phase, comprising mainly water, water-soluble materials and dispersed fine solids, such as clays;    3) an inorganic particulate phase, mainly comprising sand; and    4) an organic particulate phase, mainly comprising precipitated asphaltenes, with water and clays incorporated into the aggregate structure of the asphaltenes.
A dilute bitumen phase which is partially deasphalted and substantially free of mineral solids and water is produced as overflow in the CCD process. An aqueous phase comprising water, mineral solids, and rejected asphaltenes may be withdrawn from the CCD circuit as underflow.
The underflow obtained from the CCD process, the CCD tailings, also contains solvent. The solvent can be recovered from the CCD tailings in a tailings solvent recovery unit and the remaining underflow containing water, mineral solids and precipitated asphaltenes is deposited into a tailings pond.
Most oil sands processing operations generally result in substantial volumes of wet tailings. The wet tailings require significant handling expenditures and severely constrain overall mine planning flexibility. In addition, wet tailings present an environmentally challenging situation. In many current open-pit mining operations, waste streams are disposed of by pipelining the waste stream slurry to an external tailings confinement facility or pond, also known as a tailings pond, which is essentially a man-made pond enclosed within a dyke system that contains the waste material. Poor settling characteristics of fine inorganic solids in the containment facility or pond create an uppermost solids layer that has limited bearing capacity. The low bearing capacity of the top layer of the tailings ponds presents a technical barrier to reclaiming mined surfaces because the top layer cannot be covered with overburden using heavy earth moving machinery.
In addition to problems associated with wet tailings, many of the oil sands processing operations currently being employed use large amounts of input water. The input water is usually drawn from natural sources such as rivers that must also provide sufficient volumes to meet the competing needs of nearby communities and industrial entities. Therefore, it would be desirable to use a process for extracting bitumen from oil sands which does not employ large quantities of water.
Since as early as the 1920s, there have been many attempts to develop a non-aqueous extraction process that could be used in the oil sands mining industry. A non-aqueous extraction process could potentially reduce or eliminate the need for added process water, and result in the production of dry tailings. Dry tailings are more amenable to land reclamation efforts as compared to wet tailings. However, none of the proposed non-aqueous extraction processes have proven to be commercially viable or have addressed certain technical limitations inherent in each proposed solution.